[m-dev.] Proposing a new grade component.

[Paul Bone]

Currently the analysis for automatic parallelism is attached to the deep
profiler.  This means that a deep profiling grade is required, such as
asm_fast.gc.profdeep, and coverage profiling is also mandatory.

The following options are also relevant:

    --coverage-profiling
        This enables coverage profiling, which is normally disabled.  We could
        enable this by default but it's not useful by itself.

    --profile-optimized
        Deep profiling normally disables some optimizations, such as inlining,
        this is done so that the profile looks more like the code that the
        programmer wrote.  However, when using feedback analysis we want a
        profile that is closer to the compiled code rather than the source
        code.  This switch re-enables these disabled optimizations.  This
        option makes it a lot more likely that auto parallelization will
        succeed, because the feedback data will more-closely match the program
        being compiled.

    --profile-for-implicit-parallelism
        This option implies the two options above.

Because coverage profiling is only currently used by feedback analysis it isn't
useful to turn it out without also turning on --profile-optimized, which makes
it a lot harder for users to use the deep profiler.  Therefore I propose that
we introduce a new grade component option (an alternative to the profdeep grade
component) that also turns on --profile-for-implicit-parallelism.  I'd like to
call this grade component "profdeep_fb" (fb is short for feedback),
alternatively it could be called "prof_fb".  This should be a new grade
component so that it can be installed along side a normal deep profiling grade,
making it easier for us and our users to use automatic parallelism.

I would also like to propose renaming the --profile-for-implicit-parallelism
option to --profile-for-feedback.  This name reflects the more general
ability of this grade to be used for any type of profile feedback optimization,
not that any other uses for feedback analysis exist at the moment.

Should --profile-for-feedback imply --deep-profiling? so that it becomes a
grade option.

Thanks.

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